This invention relates to the transmission and reception of television programs and more particularly to the multiplexed transmission of two television programs via the same communication link.
The multiplexing of television pictures has been a subject of intensive research in recent years for a number of reasons. First, there are a limited number of communication channels available. Secondly, even when available, a channel may be available for only a limited period of time. Additionally, the individual transponders of typical communications satellites are bandwidth limited to one television broadcast at a time if the full signal-to-noise ratio is to be preserved.
Although multiplexing would be highly desirable economically, there have been a host of technical problems which have prevented the commercialization of a practical multiplexing system. The desirability of a multiplexing system, together with the technical shortcomings of prior art multiplexers, are described in U.S. Pat. Nos. 4,027,333 and 4,215,370, the contents of both being hereby incorporated by reference.
U.S Pat. No. 4,215,370 discloses a multiplexer wherein the transmitted wave comprises a series of standard interval (1/15.734 kHz) line signals, each of which includes a time-compressed line of video intelligence of the first program, a small part of the video intelligence at the beginning of the next line of the second program, and the full next line of video intelligence of the second program repeated from its beginning. The disclosed system, however, significantly increases the bandwidth of the transmitted signal beyond that of either of the original video signals.
U.S. Pat. No. 4,027,333 discloses a system wherein the odd numbered fields of one picture are transmitted in alternation with the even numbered fields of the other picture. The received field is delayed and recombined with their respective undelayed fields to recreate the two separate pictures.
U.S. Pat. No. 4,467,356 discloses a multiplexer wherein two input pictures are compressed horizontally, one to 3/4 width and the other to 1/4 width, and combined side by side to form a single picture suitable for transmission over a standard link. The two signals are interchanged on alternate fields.